<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>点击</button>
<script>
    const btn = document.querySelector('button');
    btn.addEventListener('click', function() {
        alert('你点击了按钮');
        });
</script>
</body>
</html>